Enhanced removal of Pb2+, Cd2+ and Zn2+ ions on porous carbon from aqueous solutions by capacitive deionization: Performance study and underlying mechanism

In this paper, nitrogen -doped porous carbon materials were successfully prepared using sucrose and activated carbon as raw materials and NH4Cl as nitrogen dopant by foaming and pyrolysis. The nitrogen -doped porous carbon (NPC-1) sample has a large specific surface area (798.425 m2/g) and good electrochemical properties. Capacitive deionization (CDI) tests showed that the removal rate was over 87% and 85% in the mixture of three ions (Pb2+, Cd2+ and Zn2+), when the initial concentration of ternary mixed solution was 10 mg/L and 20 mg/L and the voltage was 1.2 V. Density -functional -transfer theory (DFT) calculations revealed that materials containing pyridine -N and pyrrolic-N have better adsorption properties for Pb2+, Cd2+ and Zn2+ than materials containing graphite -N and materials without doped nitrogen. Meanwhile, the adsorption energy of pyridine -N and pyrrolic-N models for Pb atom are larger than those of pyridine -N and pyrrolic-N models for Cd and Zn atoms. This indicated that the NPC-1 electrode has better electrosorption capacity for Pb2+, which was consistent with the experimental results. After twenty cycles experiments, the NPC-1 electrode maintained a high removal rate for Pb2+ (95%), Cd2+ (82%), and Zn2+ (87%). This showed that the electrode material has a good recycling regeneration ability.